Defense lawyers for Nicholson hope they can convince the jury to spare his life. The same jury convicted Nicholson last week of killing his wife, Gloria, and Sharpsburg Police Chief Wayne Hathaway.
Nicholson's attorneys are called mental health professionals to testify on Nicholson's behalf.
Tuesday morning, witnesses testified that Nicholson has a low intelligence level and may be mentally retarded. Odds are, they say, Nicholson's social and communication skills have not changed much since he was a small child.
Gloria Nicholson's stepfather, Marvin Badger, says the defense is grasping at straws, and he hopes the decision comes quickly.
"I want them to come back with a verdict of death," Badger said. "He hasn't shown any remorse at all. His family hasn't shown any remorse at all. They have never called the house and said they were sorry about what happened."
Nicholson is one of 15 children. Two of his sisters have not yet testified in his behalf.
The prosecution finished presenting witnesses Monday.